Integrated circuits (ICs) such as processors are manufactured in various types of packages. In one type of package, the IC is provided as a semiconductor die that is housed within the package and the package serves to encapsulate and protect the die and to provide connectivity between the IC implemented by the die and a device, such as a computer, within which the circuit is installed.
Tin-based solder connections may be used to electrically connect the die to the package, using a structure such as a ball grid array (BGA) or pin grid array (PGA), in a flip-chip process. The flip-chip process is used to electrically connect the die to the package carrier. The package carrier, such as a substrate or a leadframe, then provides the connection from the die to the exterior of the package. The interconnection between the die and the carrier in flip chip packaging is made through a conductive “bump” that is placed directly on the die surface. That bump may be formed of copper. The bumped die is then flipped over and aligned with tin-based solder bumps formed on the package carrier. The copper bumped die is attached to the package carrier through a metallic bond formed between the copper bumps on the die and the tin-based solder bumps on the package carrier. This metallic bond is formed by reflowing the tin-based solder to attach the solder to the copper bumps on the die. The direct contact of the copper of the copper bumps with the tin-based solder causes the diffusion of the copper from the copper bumps and the tin from the solder to form copper-tin intermetallic compounds, which are necessary for a solid metallic bond. However, excessive compound build-up has detrimental effects such as the creation of a brittle bond, high bump contact resistance and high joule heating. The diffusion of the copper and of the tin creates voids within the connection between the die and the package carrier. The voids cause shorts, excessive heat, and may cause eventual failure of the device.